EP2372093B1 - Seal design on a shroud of a turbine blade - Google Patents

Description

Technical area

The invention relates to a device on a shroud provided on a turbine blade tip, with a radially to the axis of rotation about which the turbine blade is rotatably disposed, the shroud locally superior, ridge-like trained sealing structure having an oriented in the direction of rotation of the turbine blade longitudinal extent, itself has tapered with increasing radial distance to the shroud and one of the turbine blade radially facing away, flat-shaped end face.

State of the art

Turbine blades are usually provided with a shroud at their turbine blade tips which provides a vibration reducing effect on the respective turbine blade and thus contributes to extending the life of the turbine blade. In addition, at least one of the end-side shroud surface in the radial direction to the rotation axis frontally superior, rib-like sealing structure is provided, which extends in the direction of rotation to the rotational movement of the turbine blades along the shroud.

Such sealing structures serve primarily to reduce leakage flow that forms along the flow channel between the turbine blade tips and the stationary turbine housing and that does not contribute to the power gain of the turbine. The foregoing sealing structures are based on abrasive materials and, by rotating the turbine blades and due to their radial superiority to the shrouds, into a turbine wall blade tip radially opposed abradable wall structure on the turbine housing, which is typically formed in a honeycomb structure, forming a circumferential direction extending, groove-shaped recess to be ground in such a way that although the end-side shroud surface includes a minimal gap with the wall structure, however, the rib-like sealing element protrudes almost accurately into the self-machined by the sealing element groove-shaped recess. In axial projection thus concludes each blade tip with its, engaging in the groove-shaped recess sealing structure for a flowing axially through the turbine gaseous working fluid largely gas-tight.

Vibration tests performed on turbine blades, however, showed that almost completely suppressing any leakage flow leads to severe vibration instabilities along the rotating turbine blade blades.
However, such vibrations can be significantly reduced if a leakage flow can form between the turbine blade tips and the turbine housing.

Thus, it is important to look for the most balanced possible relationship between the two competing phenomena, in order to minimize the lossy leakage currents on the one hand and the occurrence of structure-weakening vibrations on the other hand.

For this purpose, a cross-sectional shape is axially, that is, provided transversely to the direction of rotation, locally magnifying cutting structure on the cover band radially projecting rib-like sealing structure, which typically has a substantially constant cross-sectional shape in the longitudinal direction, on both axially opposite flanks of the sealing structure in the direction of rotation having facing cutting surfaces. The axially projecting from the sealing structure cutting surfaces assets within the usually designed as a honeycomb structure abreibbaren turbine housing wall in comparison to the rest of the axial sealing structure width einzusträgen a wider sized groove-shaped recess, so that the sealing structure can not fit over its entire length to the groove-shaped recess fit and thus by the resulting intermediate gap between the sealing structure and groove-shaped recess can form a metered adjustable leakage current.

In addition, the rib-like sealing structure provided on the shroud in the radial direction along the turbine blade usually does not coincide with the radial center of gravity of the turbine blade, whereby additional load moments occur, especially at high speeds and high process temperatures, in the connection area between the shroud and the turbine blade increased creep rates and ultimately lead to material failure.

To meet this load problem is in the US 2004/0208743 A1 or the EP 1 507 066 A2 has been proposed to arrange the cutting structures provided on the rib-like sealing structure largely centrally of the longitudinal axis of the rib-like sealing structure, wherein the cutting structure should be as close as possible to the radial center of gravity position of the turbine blade. This measure reduces the entry of increased bending moments and mechanical stresses on the blade and shroud, one outside the center of gravity position would otherwise cause additional mass of the cutting structure. In FIG. 3 the US application and in Figure 6 of said EP-document is shown in each case a radial plan view of the rib-like sealing structure relative to the shroud, which has a V-shaped taper with increasing radial distance from the shroud in cross-section and at the mutually facing side edges respectively a raised over the respective side edge cutting surface, which occupy different staggered positions in the longitudinal extent of the rib-shaped structure. The removable from the above document combination of a shroud of a turbine blade radially superior rib-like sealing structure and attached to the sealing structure cutting structure, which is mounted as close to the radial center of gravity line of the turbine blade, only, in turbine blades up to a certain maximum size the operational Vibration behavior and the associated material stresses, especially in the area of the blade tip to influence positively. However, if longer and thus larger turbine blades are required, the shrouds take a considerable oriented in the direction of rotation length measure, which corresponds to that of the oriented in the circumferential direction rib-like sealing structure that spans the shroud comparable to a bridge or a bow, so occur in the radial direction considerable bending loads, which lead to high mechanical loads in the shroud area. To withstand these undesirably high bending loads, it offers at best, the rib-like sealing structure according to EP 1 507 066 A2 to enlarge, that is, to increase height and width. However, such a measure leads to a considerable increase in mass as well as to a deterioration of the Einschleifeigenschaften the longitudinal edges of the rib-like sealing structure provided cutting contours.
Another variant of a lace cover tape with substantially centrally arranged cutting teeth is in US 2005/0129519 A1 disclosed.

Subject of the DE 10 2008 023 424 A1 is a method of extending the life of turbine blades equipped with a tip shroud and generic sealing devices by reducing their mechanical stress during operation. In order to achieve this reduction of the mechanical stress, cutting teeth arranged at one end are to be removed and replaced by centrally arranged cutting teeth, in particular arranged inside the blade leaf.

Presentation of the invention

The invention has for its object to reduce the problem described above in the creation of larger-sized turbine blades and to optimize the area of the shroud with a sealing structure provided thereon, both in terms of their capacity and in terms of mass reduction. In particular, it is necessary to look for measures by which reduces the operational stresses and strains occurring in the turbine blade tip area and thus ultimately the turbine blade life can be significantly increased.

The solution of the problem underlying the invention is specified in claim 1. The concept of the invention advantageously further features are the subject of the dependent claims and the further description refer, in particular with reference to the illustrated embodiment.

• ein erster Flächenabschnitt I ist von zwei parallel zur Längsachse verlaufenden Seitenkanten 1, 2 begrenzt, die einen gegenseitigen Abstand f1 besitzen und von denen sich, gemessen von einer ersten Bezugsebene B1, die die Längsachse L orthogonal schneidet und die Stirnfläche St in Umlaufrichtung U am hinteren Ende begrenzt, die erste Seitenkante 1 bis zu einem Abstand a1 und die zweite Seitenkante 2 bis zu einem Abstand a2 erstrecken, wobei die zweite Seitenkante 2 von der ersten Bezugsebene B1 beabstandet ist und mit der ersten Seitenkante 1 über eine, gegenüber der Längsachse L geneigt orientierte, hintere Begrenzungskante 3 verbunden ist,
• ein zweiter Flächenabschnitt II ist von zwei gegenüber der Längsachse L geneigt verlaufenden Seitenkanten 4, 5 begrenzt, von denen die erste Seitenkante 4 sich vom Abstand a1 bis zum Abstand b1 und die zweite Seitenkante 5 sich vom Abstand a2 bis zum Abstand b2, jeweils gemessen von der ersten Begrenzungsebene B1, erstrecken,
• ein dritter Flächenabschnitt III ist von zwei parallel zur Längsachse L verlaufenden Seitenkanten 6, 7 begrenzt, die einen gegenseitigen Abstand f2 besitzen, von denen die erste Seitenkante 6 mit der ersten Seitenkante 4 des zweiten Flächenabschnittes II und die zweite Seitenkante 7 mit der zweiten Seitenkante 5 des zweiten Flächenabschnittes II verbunde sind,
• ein vierter Flächenabschnitt IV ist von zwei gegenüber der Längsachse L geneigt verlaufenden Seitenkanten e1, e2, den so genannten Schneidkanten, begrenzt, von denen die erste Schneidkante e1 sich vom Abstand d1 bis zum Abstand c1 und die zweite Schneidkante e2 sich vom Abstand d2 bis zum Abstand c2, jeweils gemessen von einer zweiten Begrenzungsebene (B2), erstrecken, die die Längsachse L orthogonal schneidet und die Stirnfläche St in Umlaufrichtung U am vorderen Ende begrenzt,
• ein fünfter Flächenabschnitt V ist von zwei parallel zur Längsachse L verlaufenden Seitenkanten 8, 9 begrenzt, die einen gegenseitigen Abstand f3 besitzen und von denen sich, gemessen von der zweiten Bezugsebene B2, die erste Seitenkante 8 bis zu einem Abstand c1 und die zweite Seitenkante 9 bis zu einem Abstand c2 erstrecken, wobei die erste Seitenkante 8 von der zweiten Bezugsebene B2 beabstandet ist und mit der ersten Seitenkante 9 über eine gegenüber der Längsachse L geneigt orientierte vordere Begrenzungskante 10 verbunden ist, und wobei gilt:
  • S = 45 mm bis 200 mm
  • a1 < a2 und 1/16 S ≤ (a1, a2) ≤ ½ S
  • b1 < b2 und 1/16 S ≤ (b1, b2) ≤ ½ S
  • c1 < c2 und 1/16 S ≤ (c1, c2) ≤ ½ S
  • d1 < d2 und 1/16 S ≤ (d1, d2) ≤ ½ S
  • f3 < f1 und 1/62 S ≤ (f1, f3) ≤ 1/14 S
  • 1/42 S ≤ f2 ≤ 1/5 S.

According to the solution, the rib-like sealing structure which projects over the shroud of a turbine blade tip locally in the radial direction to the rotation axis about which the turbine blade is arranged rotatably, which has a longitudinal extent (S) oriented in the direction of rotation (U) of the turbine blade and with increasing radial distance conically tapered to the shroud, one of the turbine blade radially facing away, just trained end face St on, which has a base surface shape, in FIG. 1 illustrated and is divided in the circumferential direction U in five contiguous surface sections I to V, which extend along a circumferentially U-oriented longitudinal axis L in the following manner:

• a first surface section I is delimited by two side edges 1, 2 extending parallel to the longitudinal axis, which have a mutual distance f1 and of which, measured orthogonally from a first reference plane B1, which intersects the longitudinal axis L and the end face St in the circumferential direction U at the rear End limited, the first side edge 1 to a distance a1 and the second side edge 2 extend to a distance a2, wherein the second side edge 2 is spaced from the first reference plane B1 and with the first side edge 1 via a, with respect to the longitudinal axis L inclined oriented, rear boundary edge 3 is connected,
• a second surface portion II is bounded by two opposite the longitudinal axis L inclined side edges 4, 5, of which the first side edge 4 from the distance a1 to the distance b1 and the second side edge 5 from the distance a2 to the distance b2, each measured from the first boundary plane B1, extend,
• a third surface section III is delimited by two side edges 6, 7 running parallel to the longitudinal axis L, which have a mutual distance f2, of which the first side edge 6 with the first side edge 4 of the second surface section II and the second side edge 7 with the second side edge 5 of the second surface section II are composites,
• a fourth surface section IV is delimited by two side edges e1, e2, which are inclined with respect to the longitudinal axis L, the so-called cutting edges, of which the first cutting edge e1 extends from the distance d1 to the distance c1 and the second cutting edge e2 from the distance d2 to the first Distance c2, measured in each case from a second boundary plane (B2), which orthogonally intersects the longitudinal axis L and limits the end face St in the circumferential direction U at the front end,
• a fifth surface section V is delimited by two side edges 8, 9 running parallel to the longitudinal axis L, which have a mutual distance f3 and from which, measured from the second reference plane B2, the first side edge 8 up to a distance c1 and the second side edge 9 extend to a distance c2, wherein the first side edge 8 is spaced from the second reference plane B2 and is connected to the first side edge 9 via a front boundary edge 10 inclined relative to the longitudinal axis L, and where:
  • S = 45 mm to 200 mm
  • a1 <a2 and 1/16 S ≤ (a1, a2) ≤ ½ S
  • b1 <b2 and 1/16 S ≤ (b1, b2) ≤ ½ S
  • c1 <c2 and 1/16 S ≤ (c1, c2) ≤ ½ S
  • d1 <d2 and 1/16 S ≤ (d1, d2) ≤ ½ S
  • f3 <f1 and 1/62 S ≤ (f1, f3) ≤ 1/14 S
  • 1/42 S ≤ f2 ≤ 1/5 p.

According to the solution, it could be shown that with a rib-like sealing structure, its radially end-side end face St is the one in FIG. 1 illustrated surface geometry, two positive effects are achieved, namely on the one hand, an improved stiffening of the rib-like sealing structure in the circumferential direction U and on the other hand, an improved cutting action of the rib-like sealing structure within the abradable turbine housing wall material. The former effect leads to a significantly higher mechanical strength of the sealing structure, which ultimately results from an axial broadening of the sealing structure provided centrally to the longitudinal extent of the rib-like sealing structure. In this central region, the sealing structure has an axial width f2, for which the following applies: 1/42 S ≦ f2 ≦ 1/5 S. On the other hand, the axial width of the sealing structure in the circumferential direction before the above central widening measures only 1/62 S ≦ f3 On the other hand, the improved cutting effect is due to the cutting edges e1 and e2 facing in the direction of rotation, which serve as transition areas between the rib area narrow in the axial extent in the fifth embodiment Surface section with a web width f3 and the axially much wider formed third surface portion with an axial rib width f2 serve.

Advantageously, at least the cutting edges e1, e2 are coated with a surface-hard layer, such as, for example, Cr ₂ C or CBN (cubic crystalline boron nitride). The coating process is preferably carried out by means of a galvanic deposition, a plasma deposition, a spray deposition or by means of a welding or soldering operation.

In FIG. 2 is a perspective view of the shroud D of a not further illustrated turbine blade shown for qualitative illustration of the solution formed sealing structure. The sealing structure DS according to the invention is preferably connected in one piece to the shroud D and rises above the shroud D with side edges 1 'to 10' which correspond in each case to the side edges 1 to 10 bordering the end face St. In this connection, it should be noted that the cutting edge surfaces e1 'and e2' associated with the cutting edges e1 and e2 are provided with the surface hardening layer (11) for improving the cutting action. Advantageously, the cut surface 10 'may also be provided with a corresponding surface hard layer (11). In a particularly advantageous manner, however, all side edge surface with a corresponding coating, so in particular the end face St, be provided with the surface-hard layer.

The from the FIGS. 1 and 2 removable seal structure DS formed in an advantageous embodiment, a longitudinal extent S, which corresponds to the oriented in the direction of rotation U shroud length. Depending on the shape and size of the shroud, a plurality of sealing structures DS formed in accordance with the invention can be arranged on the surface of a shroud D, so that they are preferably arranged next to one another in the circumferential direction.

Advantageously, the side edges 1, 4, 6, e1 and 8 of the suction side and the side edges 2, 5, 7, e2 and 9 facing the pressure side of the turbine blade blade facing. In addition, the location corresponds to the in FIG. 1 Illustrated longitudinal axis L through the end face St of the solution formed according to rib-like sealing structure at the same time also the radial center of gravity plane of the turbine blade.

In FIG. 3 is a cross-sectional view taken along in FIG FIG. 2 indicated section plane A shown. Out FIG. 3 can be seen that the side edges 6 'and 7' each with the orthogonal to the shroud surface an angle α, β include, which may typically be in the range between 0.1 ° and 45 °. The same angle of inclination also applies to the side flanks 8 'and 9'.

In FIG. 4 is a cross-sectional view represented by a cutting contour. Not necessarily, it is necessary to provide the entire surface of the cutting contour with a hard surface layer 11. At the very least, it is necessary to coat those surface area of the cutting contour with the surface-hardened layer 11 which comes into engagement with the abradable material on the turbine housing wall. For this purpose, it is advantageous to provide an effective layer thickness Z of 0.1 mm to 4.5 mm on the cutting surface, which has at least one penetration depth P1, with which the cutting contour is able to penetrate into the abradable material. Typically, the cutting depth P1 is about 0.5 mm to 15 mm. The layer is thinned over a further region P2 which extends between P1 + 0.5 mm to 15 mm.

LIST OF REFERENCE NUMBERS

1 to 10

side edges

e1, e2

cutting edges

B1

Rear boundary plane

B2

In the direction of circulation front boundary plane

1 ', ... 10'

Side edge surfaces

e1 ', e2'

Cutting edge surfaces

D

shroud

DS

sealing structure

S

Length of the sealing structure

f1, f2, f3

Axial width of the sealing structure

Z

Layer thickness for a surface-hardened layer

11

Surface hard coating

P1, P2

coating parameters

Claims (12)

1. A device on a shroud provided on a turbine blade tip, with a sealing structure designed like a line of ribs, locally projecting over the shroud radially to the rotational axis around which the turbine blade is rotatably arranged, which sealing structure has a longitudinal extent (S) oriented in the direction of rotation (U) of the turbine blade, tapers with increasing radial distance to the shroud, and terminates with a flat formed end face (St) which radially faces away from the turbine blade and in the direction of rotation is divided into interrelated surface sections (I, II, III, IV, V) which, in the following way, extend along a longitudinal axis (L) oriented in the direction of rotation (U):

   - a first surface section (I) is delimited by two side edges extending parallel to the longitudinal axis, which have a mutual spacing f1 and of which a first side edge (1) extends to a distance a1 and a second side edge (2) extends to a distance a2, measured from a first reference plane (B1) which orthogonally intersects the longitudinal axis (L) and delimits the end face (St) at the rear end in the direction of rotation (U), wherein the second side edge (2) is at a distance from the first reference plane (B1) and is connected to the first side edge (1) via a rear delimiting edge (3) which is oriented in an inclined manner in relation to the longitudinal axis (L),

   - a second surface section (II) is delimited by two side edges (4, 5) extending in an inclined manner in relation to the longitudinal axis (L), of which a first side edge (4) extends from the distance a1 to the distance b1 and a second side edge (5) extends from the distance a2 to the distance b2, measured in each case from the first reference plane (B1),

   - a third surface section (III) is delimited by two side edges (6, 7) extending parallel to the longitudinal axis (L), which have a mutual spacing f2 and of which a first side edge (6) is connected to the first side edge (4) of the second surface section (II) and a second side edge (7) is connected to the second side edge (5) of the second surface section (II),

   - a fourth surface section (IV) is delimited by two side edges e1, e2, the so-called cutting edges, extending in an inclined manner in relation to the longitudinal axis (L), of which a first cutting edge (e1) extends from the distance d1 to the distance c1 and a second cutting edge (e2) extends from the distance d2 to the distance c2, measured in each case from a second reference plane (B2) which orthogonally intersects the longitudinal axis (L) and delimits the end face (St) at the front end in the direction of rotation (U),

   - a fifth surface section (V) is delimited by two side edges (8, 9) extending parallel to the longitudinal axis (L), which have a mutual spacing f3 and of which a first side edge (8) extends to a distance c1 and a second side edge (9) extends to a distance c2, measured from the second reference plane (B2), wherein the first side edge (8) is at a distance from the second reference plane (B2) and is connected to the first side edge (9) via a front delimiting edge (10) which is oriented in an inclined manner in relation to the longitudinal axis (L), characterized in that the following applies to its geometry parameters S, a1, a2, b1, b2, c1, c2, d1, d2, f1, f2, f3:

   S = 45 mm to 200 mm

   a1 < a2 and 1/16 S ≤ (a1, a2) ≤ ½ S

   b1 < b2 and 1/16 S ≤ (b1, b2) ≤ ½ S

   c1 < c2 and 1/16 S ≤ (c1, c2) ≤ ½ S

   d1 < d2 and 1/16 S ≤ (d1, d2) ≤ ½ S

   f3 < f1 and 1/62 S ≤ (f1, f3) ≤ 1/14 S

   1/42 S ≤ f2 ≤ 1/5 S.
2. The device as claimed in claim 1,
   characterized in that at least the side edges e1 and e2 are coated with a surface-hardened coating (11) and serve as cutting structures.
3. The device as claimed in one of claims 1 to 2,
   characterized in that the first and second side edges (1, 2, 6, 7) in each case of the first and third surface sections are arranged at a distance to the longitudinal axis (L), and
   in that the longitudinal axis (L) aligns with the first side edge (8) of the fifth surface section (V).
4. The device as claimed in one of claims 1 to 3,
   characterized in that the sealing structure designed like a line of ribs has side flanks extending in an inclined manner in relation to a shroud surface which is assignable to the shroud, the inclinations of which face each other in each case, and in that the side flanks by their radially upper edges delimit the end face (St).
5. The device as claimed in one of claims 1 to 4,
   characterized in that side flanks, which are inclined in relation to a shroud surface which is assignable to the shroud, are assignable in each case to the first and second side edges (6, 7) of the third surface section (III), which inclined side flanks in each case include an inclination angle of between 0.1° and 45° with the orthogonals to the shroud surface.
6. The device as claimed in one of claims 1 to 5,
   characterized in that the longitudinal extent (S) of the sealing structure designed like a line of ribs corresponds to the shroud length which is oriented in the direction of rotation (U).
7. The device as claimed in one of claims 1 to 6,
   characterized in that at least two sealing structures designed like a line of ribs are attached on a shroud of a turbine blade.
8. The device as claimed in claim 7,
   characterized in that the at least two sealing structures are attached on the shroud of the turbine blade next to each other in the direction of rotation.
9. The device as claimed in one of claims 1 to 8,
   characterized in that the sealing structure designed like a line of ribs is provided with a surface-hardened coating (11) at least in surface sections.
10. The device as claimed in claim 9,
    characterized in that the surface-hardened coating (11) has a coating thickness of up to 4.5 mm.
11. The device as claimed in one of claims 1 to 10,
    characterized in that the surface-hardened coating (11) consists of Cr₂C or CBN.
12. The device as claimed in one of claims 1 to 11,
    characterized in that the side edges 1, 4, 6, e1 and 8 face the suction side of the turbine blade and the side edges 2, 5, 7, e2 and 9 face the pressure side.

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